Oracle SQL Developer

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Overview of Triggers9.1.1 Types of Triggers9.1.2 Naming TriggersA trigger is either a stored PL/SQL block or a PL/SQL, or C procedure associated witha table, view, schema, or the database itself. Oracle automatically executes a triggerwhen a specified event takes place, which usually is a DML statement being issuedagainst the table.You can create triggers to be fired on any of the following:■ DML statements (DELETE, INSERT, UPDATE)■■DDL statements (CREATE, ALTER, DROP)Database operations (LOGON, LOGOFF)Trigger names must be unique with respect to other triggers in the same schema.Trigger names do not need to be unique with respect to other schema objects, such astables, views, and procedures. For example, a table and a trigger can have the samename; however, to avoid confusion, this is not recommended.9.1.3 When Is the Trigger Fired?A trigger is fired based on a triggering statement, which specifies:■The SQL statement or the system event, database event, or DDL event that firesthe trigger body. The options include DELETE, INSERT, and UPDATE. One, two, orall three of these options can be included in the triggering statement specification.■ The table, view, DATABASE, or SCHEMA associated with the trigger.If a trigger contained the following statement:AFTER DELETE OR INSERT OR UPDATE ON employees ...then any of the following statements would fire the trigger:DELETE FROM employees WHERE ...;INSERT INTO employees VALUES ( ... );INSERT INTO employees SELECT ... FROM ... ;UPDATE employees SET ... ;An UPDATE statement might include a list of columns. If a triggering statementincludes a column list, the trigger is fired only when one of the specified columns isupdated. If a triggering statement omits a column list, the trigger is fired when anycolumn of the associated table is updated. A column list cannot be specified forINSERT or DELETE triggering statements.9.1.4 Controlling When a Trigger Is FiredThere are several ways to control when a trigger is fired.9.1.4.1 Firing Triggers With the BEORE and AFTER OptionsThe BEFORE or AFTER option in the CREATE TRIGGER statement specifies exactlywhen to fire the trigger body in relation to the triggering statement that is being run. Ina CREATE TRIGGER statement, the BEFORE or AFTER option is specified just before thetriggering statement.In general, you use BEFORE or AFTER triggers to achieve the following results:9-2 SQL Developer Online Help
Overview of Triggers■■Use a BEFORE row trigger to modify the row before the row data is written to disk.Use an AFTER row trigger to obtain, and perform operations, using the row Id.Note: BEFORE row triggers are slightly more efficient than AFTERrow triggers. With AFTER row triggers, affected data blocks must beread (logical read, not physical read) once for the trigger and thenagain for the triggering statement. Alternatively, with BEFORE rowtriggers, the data blocks must be read only once for both the triggeringstatement and the trigger.If an UPDATE or DELETE statement detects a conflict with a concurrent UPDATE, thenOracle performs a transparent ROLLBACK and restarts the update. This can occurmany times before the statement completes successfully. Each time the statement isrestarted, the BEFORE statement trigger is fired again. The rollback does not undochanges to any package variables referenced in the trigger. Your package shouldinclude a counter variable to detect this situation.9.1.4.2 Firing Triggers With the FOR EACH ROW OptionThe FOR EACH ROW option determines whether the trigger is a row trigger or astatement trigger. If you specify FOR EACH ROW, then the trigger fires once for each rowof the table that is affected by the triggering statement. These triggers are referred to asrow-level triggers.The absence of the FOR EACH ROW option indicates that the trigger fires only once foreach applicable statement, but not separately for each row affected by the statement.These triggers are referred to as statement-level triggers and are useful for performingvalidation checks for the entire statement.9.1.4.3 Firing Triggers Based on Conditions (WHEN Clause)An optional trigger restriction can be included in the definition of a row trigger byspecifying a Boolean SQL expression in a WHEN clause.If included, then the expression in the WHEN clause is evaluated for each row that thetrigger affects. If the expression evaluates to TRUE for a row, then the trigger body isfired on behalf of that row.The expression in a WHEN clause must be a SQL expression, and it cannot include asubquery. You cannot use a PL/SQL expression (including user-defined functions) inthe WHEN clause. A WHEN clause cannot be included in the definition of a statementtrigger.9.1.5 Accessing Column Values in Row TriggersWithin a trigger body of a row trigger, the PL/SQL code and SQL statements haveaccess to the old and new column values of the current row affected by the triggeringstatement. Two correlation names exist for every column of the table being modified:one for the old column value, and one for the new column value. These columns in thetable are identified by :OLD.colum_name and :NEW.column_name.Depending on the type of triggering statement, certain correlation names might nothave any meaning.■A trigger fired by an INSERT statement has meaningful access to new columnvalues only. Because the row is being created by the INSERT, the old values arenull.Triggers: Usage Information 9-3
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Oracle SQL DeveloperOnline HelpRele
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Contents1 SQL Developer Concepts an
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3.12 Create/Edit Index ............
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6.3.2 Updating Data With the UPDATE
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10.2.5 SQL*Plus SET Commands.......
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SQL Developer User InterfaceThe men
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SQL Developer User InterfaceThe Com
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Database Objects1.2 Database Object
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Database Objectscontaining the mast
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Database Objects■■■■■■
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Database ConnectionsWhen you start
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Running and Debugging Functions and
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Using the SQL WorksheetRelated Topi
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Using the SQL WorksheetScript Runne
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Using the SQL Worksheetmentioned in
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Reports1.9 ReportsRelated TopicsRun
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Reports1.9.3 Table reportsTable rep
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Reportsissues and vulnerabilities,
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SQL Developer Preferencesand the SQ
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SQL Developer Preferences1.10.3 Cod
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SQL Developer PreferencesSQL Develo
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SQL Developer User Information: Loc
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Supplementary Oracle Database Infor
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Creating a Table (Books)the table t
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Creating a Table (Transactions)Colu
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Creating a SequenceName: for_key_bo
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Creating a PL/SQL Procedure2.6 Crea
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Using the SQL Worksheet for Queries
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Script for Creating and Using the L
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Script for Creating and Using the L
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Check for UpdatesTo remove the effe
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Select Library3.8 Select LibraryThi
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Create PL/SQL Function, Procedure,
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Create Table (quick creation)Relate
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Create/Edit Table (with advanced op
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Create Type (User-Defined)For more
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Create/Edit ViewTest Syntax: Checks
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Configure File Type AssociationsDia
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Find/Replace TextTo add a type of o
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Save/Save As3.37 Save/Save As3.38 S
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SQL*Plus Location3-28 SQL Developer
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Managing TablesTo include lowercase
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Managing Tables4.2.4 Column Constra
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Managing Indexes4.3 Managing Indexe
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Managing Indexesuseful when all of
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Managing Views4.4 Managing Views4.3
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Managing Synonyms4-12 SQL Developer
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Storing Numeric Data■■NCHAR and
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Storing Numeric DataThe absence of
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Storing Datetime Data5.4.1.2 Using
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Storing Datetime Data5-8 SQL Develo
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Retrieving Data With Queries■■
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Retrieving Data With QueriesSee Als
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Page 128 and 129: Entering and Executing PL/SQL CodeY
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Page 148 and 149: Handling PL/SQL ErrorsTo handle une
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Page 152 and 153: Handling PL/SQL Errors7-26 SQL Deve
Page 154 and 155: Overview of Packages and Subprogram
Page 156 and 157: Managing Packagescalling procedures
Page 158 and 159: Oracle Product-Specific PackagesTab
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Page 162 and 163: Oracle Product-Specific Packages8-1
Page 166 and 167: Overview of Triggers■■A trigger
Page 168 and 169: Designing TriggersNote: A procedure
Page 170 and 171: Using SQL*Plus■■■Running Scri
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Page 176 and 177: Overview of Globalization Support
Page 178 and 179: Setting up the Globalization Suppor
Page 192 and 193: SQL and PL/SQL Programming with Uni
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Page 196 and 197: Locale-Dependent SQL Functions with
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Page 200 and 201: COLLECTION_IS_NULL exception, 7-22c
Page 202 and 203: overview, 7-14EXPLAIN PLANexecution
Page 204 and 205: NLSSORT SQL function, 11-21NO_DATA_
Page 206 and 207: displaying output from PL/SQL, 7-9s
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Oracle SQL Developer

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